575 throwing chain from middle to granny . Why?

Only does it on the top 2 cogs of the cassette, its fine on the lower 7. Riding along on anything bumpy and it just ghosts on its own from middle to granny.
I have not changed anything or dropped it recently, but its started happening over the last 3 rides or so.
Checked for bent teeth on the middle ring , checked angle of fr mech, played about with barrel adjuster on fr mech and am almost certain its not lifting the chain off and dumping it down to granny.